The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Varying power demands (e.g. stop-and-go driving and/or quick acceleration) in a conventional propulsion system may cause the system to operate inefficiently. For example, the conventional propulsion system may include an internal combustion engine. Inefficiencies in the engine lead to increased fuel consumption and increased emissions.
A hybrid electric vehicle (HEV) merges features of the conventional propulsion system with those of an electrical vehicle system. For example, the HEV may include the conventional propulsion system and an on-board rechargeable energy storage system (RESS) that improves fuel economy and performance. The conventional propulsion system and/or a regenerative brake provide energy to the RESS, which stores the energy for later use. The RESS uses the stored energy to drive the vehicle during acceleration periods. Consequently, the conventional propulsion system operates only when at optimum efficiency. The RESS may include a bank of batteries to provide storage. Typically, improvement in fuel economy of the vehicle corresponds to storage capacity and other characteristics of the RESS.